1. Field of the Invention
This invention is generally related to the field of seismic gas exploders and more particularly to devices of this character capable of delivering a series of rapid high energy acoustic pulses which may be injected into the earth. A widely known type of gas exploder manufactured under the name DINOSEIS, a Registered Trademark of Atlantic Richfield Company, utilizes a combustion chamber formed between a pair of rigid telescoping members, inlet means for introduction therein of a fuel gas and an oxidizing gas, spark means, and exhaust means for scavenging spent gases from the combustion chamber. The spark means is actuated to ignite a combustible mixture of the fuel gas and oxidizing gas so as to create an impulse adapted to drive the two rigid members apart. In use, the device either rests on the ground or is supported so that one of the rigid members impacts the ground on detonation.
If it is desired to employ a device of this character for producing a series of repetitive seismic shock waves or other similar signals, the spent gases from each shot have to be substantially removed from the chamber prior to the succeeding shot and also the two rigid members have to be returned to their original relation through gravity means, air spring return or the like. Both of these steps introduce time delays which prevent the production of acoustic pulses at a rate faster than every 1 or 2 seconds.
Another reason why a conventional gas exploder of this type is not well suited to the production of seismic pulses at a rapid repetition rate is that unless severely restrained the device will lift off the ground with each impulse. A very rapid return to earth will necessarily produce an undesirable secondary pulse which will interfere with the production of pulses of desired character and obscure the reflections therefrom. Experience has shown that when such a device is severely restrained against reactive movement away from the earth the desired detonation shock waves do not develop.
Another prior art device which produces repetitive impacts is the jackhammer. This is a basically low energy device adapted for surface penetration. It operates through the pressure of compressed air rather than detonation of an explosive mixture, which is a characteristic of the device to be described.
Also well-known is the diesel pile driver which operates through the cyclic travel of a heavy weight subjected to gravity fall. This is a high energy device which operates on diesel principle but is relatively slow in repetition rate, i.e., on the order of about three seconds per cycle.
It is therefore a general object of this invention to provide a novel form of seismic gas exploder adapted to inject high energy acoustic pulses into the earth at a high repetition rate.
It is a more specific object of this invention to provide a device of this character which is not dependent for its operation upon the reciprocal or cyclic motion of two chamber-forming members movable relative to each other.